Trade still need 15 day hold even though steam guard is activated
Steam's documentation of trade holds says:
If you're trading items with a friend, and you've been friends for more than 1 year, the hold is 1 day.
If you haven't had your account protected by a Mobile Authenticator for at least the last 7 days, items leaving your account will be held by Steam for up to 15 days. This provides you time to discover any transactions on hold that you didn't make.
So it sounds like you haven't been friends for long enough or haven't had your authenticator enabled for long enough. You just need to wait a few more days.